1. Field of the Invention
The present invention relates in general to roofing systems. In particular, the present invention relates to an improved plate for use in a plate/fastener assembly employed to secure insulation material to a roof deck.
2. Description of the Related Art
It is known to form roof systems by providing a metal roof deck. To provide protection against the elements and a thermal barrier, a layer of insulation material is placed over the metal roof deck and secured thereto by plate/fastener assemblies. These assemblies consist of a metal or plastic plates to spread the load of a fastener, which extends through the plate and insulation and is fixed to the metal roof deck. Plies of synthetic coating, tar, gravel or various roofing materials are then applied over the insulation and plate/fastener assemblies to complete the roof.
While this arrangement has been serviceable, various problems have been experienced with the plate/fastener assemblies. For example, it is difficult to maintain the fastener normal to the roof deck during insertion, the fastener is susceptible to overdriving resulting in an excessive load being exerted on the plate which leads to premature loosening, and the weight of a worker walking upon the roof may cause the plate to slide down along the fastener, such that the head of the fastener damages the coating plies which complete the roof.
Many of these problems have been solved by a plate/fastener assembly as shown in U.S. Pat. Nos. 4,361,997, issued Dec. 7, 1982, and 4,959,938, issued Oct. 2, 1990, both to DeCaro. The assembly shown in these patents includes a plate formed of plastic which essentially consists of a stress plate having a hub extending down from the bottom surface of the stress plate. The hub includes a central opening having a first diameter to receive the fastener therethrough. The fastener is an elongated member having two sections of threads. The first section of threads has a diameter such that it will pass through the opening in the hub without engagement, yet maybe employed to secure the fastener to the roofing deck. The second set of threads is adjacent the head of the fastener and has a diameter such it they will engage with the opening in the hub. This will prevent the sliding of the plate along the fastener, and additionally helps to prevent over driving of the fastener.
While this arrangement has been an improvement over other plate/fastener assemblies, it is still possible for the plate to rotate with respect to the fastener, causing loosening and possibly disengagement of the plate from the fastener. As may be envisioned, this will threaten the integrity of the roofing plies, and possibly allow the insulation to separate from the roofing deck.